ELKHART, Ind. — After days of high-stakes negotiations with foreign governments, President Trump traveled to a rally here Thursday night, briefly swapping his role as grim-faced statesman for one that comes more naturally to him: campaign trail firebrand.
In a visit meant to bolster Mike Braun, a wealthy former state legislator who won a bruising Republican Senate primary this week, Mr. Trump appeared before an excited crowd to share his administration’s track record: North Korea had freed three American prisoners. The United States had withdrawn from the nuclear agreement with Iran. And the American Embassy would soon open in Jerusalem.
The president’s message to his voters was clear — because of his efforts, “America is respected again.”
Also clear was his message to the supporters who packed the 7,300-capacity middle school gym here: That progress could quickly disappear if the balance of the Senate tips against Republicans this fall.
“This week, you nominated an incredible slate of Republican candidates,” Mr. Trump said. “And you have to work every day between now and November to elect more Republicans.”
In a speech reminiscent of his own time as a candidate, Mr. Trump disparaged a litany of opponents, saving much of his ire for Senator Joe Donnelly, the chamber’s most vulnerable Democrat, who will face Mr. Braun in November.
The president referred to Mr. Donnelly, whom he once courted but has now turned on, as “Sleepin’ Joe,” and painted Mr. Donnelly as an “incredible swamp person” emblematic of the political establishment his administration has promised to eradicate from Washington.
Mr. Trump also sampled from his classic red-meat menu, flirting with extending his presidential term, castigating the “fake news media,” promising to build a wall on the southern border with Mexico — “when I get the votes,” he said, “I need Republicans” — and espousing his reverence for the American flag.
He peppered his speech with folksy references to the Hoosier state, including basketball, the former incendiary Indiana University basketball coach Bob Knight and Lou Holtz, the former Notre Dame football coach. And for added measure, Mr. Trump brought Vice President Mike Pence, a native Hoosier and a former governor of the state, with him to the gymnasium.
(Mr. Pence’s brother, Greg, handily won the primary this week for the vice president’s former House seat. At one point, Mr. Trump ribbed the vice president, asking if his brother won by a wider margin than he had.)
Mr. Trump’s only misstep came when he praised Bill Belichick, the coach of the New England Patriots. “No, no, we like him,” Mr. Trump said to appease the booing crowd, presumably Indianapolis Colts fans.
But the crowd enthusiastically bought the president’s pitch, even if Barack Obama successfully sold that brand of flattery here first.
Elkhart, on the northern edge of Indiana, is a manufacturing town where recreational vehicle assembly has long been the bread and butter of the local economy. A decade ago, amid the Great Recession, and when the town had one of the fastest-rising unemployment rates in the United States, Mr. Obama often made campaign stops here during his primary race against Hillary Clinton.
Taking a chance on Mr. Obama’s message of hope in 2008, Indiana swung Democratic for the first time in decades.
Jobs have since returned to Elkhart, but not at the same rate of pay. People said they have a harder time scraping to the middle than they once did.
But Elkhart went from having double-digit unemployment rates to less than 3 percent, with the most drastic improvement happening while Mr. Obama was in office. On Thursday, however, the mention of Mr. Obama’s name was met with sustained jeers.
Indeed, in recent years, the state’s electoral map has veered back to the right. And Mr. Trump’s 2016 “Make America Great Again” campaign appears to have effectively steamrolled much of the Obama-era good will.
Dan Holtz, the chairman of the Elkhart County Republican Party, said in an interview that Mr. Trump’s “America First” messaging — and candidates like Mr. Braun, who carry a version of that message — resonate in a stronger way with voters than the Obama administration’s story of Elkhart’s recovery ever did.
“Elkhart has always been sort of a boom and bust town,” Mr. Holtz said. “There’s no serious person here who credits Obama with that recovery.”
Democrats in the area say Mr. Trump is trying to take credit for the past administration’s progress.
“The numbers tell a clear story, that Elkhart’s amazing recovery in many was the story of the Obama economy,” said Mayor Pete Buttigieg of South Bend, Ind., a Democrat.
Mr. Trump, he said, was leaning hard on nostalgia that somehow would magically restore the manufacturing center, which the mayor said was a false hope.
“Trying to turn the clock back socially, economically and racially to the ’50s, that’s attractive to some people,” Mr. Buttigieg said. “But the alternative is to move to the future.”
But Mr. Trump’s supporters in Indiana may have different ideas of what they want their political future to be, a point emphasized by the president and vice president during their speeches Thursday night.
“The truth is our administration has faced unprecedented obstruction by Democrats,” Mr. Pence said, “including Indiana Senator Joe Donnelly.”
Shortly after Mr. Trump left the rally, Mr. Donnelly, who was first elected to the Senate in 2012 and is considered a centrist in his party, issued a statement answering the president’s accusations that he could not be trusted to deliver on the Republican agenda. Mr. Donnelly has carefully nurtured a voting record that has, until now, avoided being considered by Republicans as too liberal.
“It’s O.K. that the president and vice president are here today for politics, but problems only get solved when you roll up your sleeves and put in the hard work,” Mr. Donnelly said. “I’m Indiana’s hired help in the Senate because I don’t work for any president or any political party — I work for Hoosiers, and that will never change.”
Mr. Donnelly may face an uphill battle persuading them. As Mr. Holtz, the local Republican chairman put it, Democrats are increasingly viewed as obstructionists in the Senate, a sign that the Trump administration’s messaging on the subject may be working at the local level.
Despite Mr. Trump’s triumphant message of recovery, “I’ve never seen people as angry as they are now” over key issues, particularly over the cost of their health care, Mr. Holtz said.
Mr. Donnelly, Mr. Pence reminded the crowd, had voted against the repeal of the Affordable Care Act.
Michael Tackett contributed reporting from South Bend, Ind.